Vacuum distillation of oils



Dec. is, 1956 G. A.4 MoYER VACUUM DISTILLATION oF oILs Filed Oct. 23,1952 United States PatentO VACUUM DIsTiLLArroN F OILS Golden A. Moyer,Bartlesville, Okla., assigner to Phillips Petroleum Company, acorporation of Delaware Application october 2s, 1952', serial No.316,411

s claims. (cl. 19e- 77) This invention relates to the vacuumdistillation of oils. In one aspect this invention relates to a processfor the vacuum distillation of heavy hydrocarbon oils. In one aspectthis invention relates to apparatus for carrying out the vacuumdistillation of oils. In another aspect this invention relates to a stepof withdrawing a portion of residuum product from a vacuum distillationzone and adrnixing same with oil feed previously heated at an elevatedtemperature for charging to the vacuum distillation zone, so as toprevent incipient cracking of the heated oil on the way to thedistillation zone, by quenching, and to provide a heat carrier toincrease the total heat available in the initial flashing operation inthe vacuum distillation zone, whereby depth of tiash is increasedwithout increasing temperature of the oil feed. In still another aspectthis invention relates to a step of recoveringV condensed product ofvacuum distillation and returning a portion of same to the distillationzone together with fresh feed and passing a remaining portion to apredetermined utility under carefully controlled constant iiow rateconditions.

Heretofore in the vacuum reduction of residual oils, distillatefractions having high carbon residues have been obtained, together withresidual pitch or tar fractionsin high yield, i. e., as for example from50-70 volume percent of residue based on the total oil charged.Furthermore, 4the distillate fractions thus recovered are dirty, thatis, they are high carbon residue oils containing heavy carbonaceousmaterials present as a result of the entrainment of such materials inthe vapors during the vacuum distillation. Such high carbon residue gasoils are undesirable as feed stock for various conversion processes.Furthermore, when employing conventional.oil-reduction operations someof the gas oil components of the oil charge are lost to the distillationresidue at the eX- pense of gas oil yield. f Y i Reduction of thepitchor tar yield depends to a large extent upon thehigh temperature andlow'pressure conditions that can be maintainedduring the initial flashdistillation or reduction step. The maximum liash temperature is limitedby cracking of the heated oil with concomitant gas formation andincreased distillation pressure, these resulting conditionsfin turnVcausing a decrease in reduction eiiiciency. It is therefore highlydesirable that a maximum flash temperature be achieved without theoccurrence of cracking, in. order tol facilitate a maximum f depth ofliashing, and in order to produce-.maximum yields of'distillate productand lowest possible yieldsofxresiduujflf v i Thisl invention providesfor the vacuum reduction of heavy oils under maximum distillationtemperatures that can. be employed without oil crackingv and -underminimum operating pressures and for the recovery of gas oil `distillatefractions particularly suitable as. feed stocks for various conversionprocesses, in higher yield, and for concomitant lower yields of pitchproduct, than have been obtained heretofore.

In accordance with a broad. embodiment .of this invention, a heavy oil,as for example a. topped crude or a Patented Dec. 18, 1956 residuum froma topped crude cracking operation or a mixture of such heavy oils,having been heated to a ternperature required for -ashing same in avacuum distillation zone, as for example 600-900 F., is introduced intoa liash or first section of an elongated distillation zone maintained atan over-allabsolute pressure generally below from 0.1 to l5 mm. Hg andoften as low as from 0.01 to 1.0 mm. Hg. The heated charge upon beingintroduced into the first section is flashed, with the highest boilingcomponents of the charge material remaining unvaporized, theseunvaporized materials comprising residual pitch, a major proportion ofwhich settles as liquid in the first section. A small portion ofunvaporized material is entrained in the ashed vapors as small, finelydivided droplets. Vapors containing entrained liquid droplets are passedfrom the liash section through a batile into and through a secondsection downstream from the iiash section and adjacent thereto, whereinat least a portion of the entrainment settles as residual liquidproduct. Liquid product in the second section contains settledentrainment and at least a portion of any condensate that may be formedin the said section by radiation. Vapors are passed from the secondsection into a downstream or third section, adjacent to it in contacttherein with a spray of cooler oil to effect partial or substantiallycomplete condensation of vapor as desired. When only partialcondensation is elfected, the vapors are passed against the flow ofatomized oil droplets so as to condense the vapor on the oil spray andas separate droplets, the oil spray having a momentumat least as high asthat of condensate formed in contact therewith so as to cause the totalcondensate to settle in the contacting section. Uncondensed vapors fromthe said third section are then passed into an adjacent or fourthsection and completely condensed therein. If desired, additional partialcondensation steps can be employed prior to effecting the final andcomplete condensation. Although when eifecting total condensation asdescribed above, alone or in conjunction with a prior partialcondensation step or steps, it is not required that the sprayed dropletsbe directed against the vapors contacted therewith, contacting thevapors against sprayed droplets under momentum conditions as discussedabove is preferred because in this manner the problem ofv condensaterecovery is simplified and the loss of condensate pressures.

Y terminates' vtherein in a direction toward the shell end 12.

My invention is` further described with reference -to the attacheddrawing which isa diagrammaticvow sheet illustrating one embodiment of aprocess of my invention and also setting forth vacuum distillationyapparatus .of my invention. Referringnowto, the drawing, inlet conduit 9extendsintoend section I of closedA elongated shell 1d, heavily,insulated b y external insulation means 11,' and A wire Vmat 13 istransversely` disposed in shell. section vI intermediate the outlet endof conduit 9fand shell end 112,. Batleld, in Ashelll() transverselycloses same and terminates. shell section'l. Ballie16. in shell10"trans.- versely closes same, is, disposed .intermediate baille' 14 Vand shell. end', 17 and; terminatesk shell section II, the

remaining portion of shell V10 constituting` section III. Spray nozzlesystem 18 in section IH comprises separate nozzle assemblies 18a, 18b,vand 18C, eachvnozzle; assembly being directed to deliver spray toward.baille (16,;,no'zzle assembly 13a being disposed in closest proximitytoy baille 16,A nozzle assemblyy 18e being furthermost from baffle 16and nozzle assembly ltb being disposed intermediatenassembliesslra and18C. Conduit 1'9" is connectedV with the interior of shell 10 throughmist extractor system Y2,1 in

section III at a point intermediate spray assembly 18 and shell end 17,and extends from shell iti to an external vacuum producing means, as forexample a steam jet system 22.

Conduit outlet means in shell l@ comprises surge vessels 23, 24, and 26,respectively connected with sections I, i, and Hl, to receive materialsdischarged from each said section. Each surge vessel, i. e., 23, 24, and26, is respectively equipped with conventional liquid level controlmechanisms, 27, 28 and 29, for regulating flow of liquid from the surgevessels through respective motor valves, 31, 32 and 33. Conduits 34, 36and 37 are connected respectively with spray assemblies 18a, 18h, and13C and with header conduit 38 and are equipped respectively withconventional flow recording controllers 39, 4l and 42 for regulatingflow of liquid through motor valves 43, 44, and 46. Conduits 47 and 4Sare connected respectively with surge vessels 26 and 23 and are eachequipped with conventional llow recording control means 49 and 51 forregulating flow of liquid through motor valves S3 and 52, respectively.

Battles i4 and i6 can be of any suitable design, such as for example aplurality of overlapping plates, a plurality of plates in separateplanes containing openings oiset from those in an adjacent plate, asystem of overlapping angle members, or the like, it being importantthat the bae provides for off-set openings necessitating a tortuous pathfor vapors passed therethrough, it also being necessary that the offsetopenings are of sufficient size so as to not develop an undue pressuredrop therethrough. One suitable form of baiie i4 and i6 constitutes asystem of angle irons comprising two parallel groups, i. e., a doublerow, of inter-locked angle irons, each group comprising a plurality ofelongated spaced members (angle iron) the central or spaced portions ofall members in one group facing those of the other, and overlapping sothat the adjacent edges of any two adjoining members in each groupconverge toward the central or face portion of a member in the oppositegroup, thus directing vapors iirst into the central or face portion of amember of the opposite group and then in a double reverse direction intothe adjacent downstream section in the chamber, thereby providing foroifset openings and a tortuous path for vapors therethrough.

Dams and 20 are associated, respectively, with baiiies 14 and 16, alonga bottom portion of shell it) to prevent flow of settled liquid from oneshell section into another. When employing baffles of the interlockedangle iron type described above, the dam is preferably disposed betweenthe two parallel groups or rows of angle irons.

Other apparatus of my invention is disclosed in the followingdescription of one embodiment of the process of this invention.

Again referring to the drawing, a heavy hydrocarbon oil such as a cycleoil resulting from distillation of product of catalytic cracking, fromline 54 together with topped crude from line 56 nand steam from line 57,is charged into line 58 and then into heater 59 wherein it is heated toa temperature within the range of about GOO-900 F. under a pressuregenerally approximating atmospheric pressure and not exceeding about 100p. s. i. g. Heated oil is discharged from coil 61 in heater 59 throughline 62 into hot oil separator 63 wherein light ends present in theheated liquid are separated and vented through line 64. Steam from line66 is admitted to separator 63 to strip vapors from the liquid therein,and is withdrawn together with vapors through line 64. Separator 63 isoperated under oil flashing conditions.

Unflashed oil in separator 63, heated to a temperature at whichincipient cracking may occur, is quenched just sufficiently to preventincipient cracking but to permit the oil to be at its maximumnon-cracking temperature. This quench is effected by introducing oilvresiduum distillation product as descibed hereinafter, in admiXture withunquenched oil in separator 63. Unashed oil,

containing residual distillation product admixed therewith, is withdrawnfrom separator 63 at its predetermined high ternperature through line 66and passed into line 9 and then into section I of vacuum distillationchamber 8 under flashing conditions against w-ire mat 12, either fromthe open end of pipe 9 or from a spray nozzle 9a attached in section lto pipe 9. in this manner, charge emitted toward mat 13 in section i iscaused to suddenly reverse its direction'of ilow, and separation ofunvaporized portions from the vaporized portion is thereby greatlyaccelerated, and droplets not vaporized coalesce on the mat with aminimum of splashing, thereby lessening the amount of liquid entrainedin the vapors. Discharge of oil against wire mat 13 in this manner alsocauses unvaporized droplets to ilow against the flow of hot vapors,which facilitates further vaporization of those liquid charge droplets,thus further providing for a decreased yield in residual unvaporizedcharge, and for increasing the yield of lighter gas oil distillate.

A portion of unvaporized oil settles in section I as residuum or pitchproduct. Residuum from section I is discharged into surge drum 23 and inpart returned as quench to separator 63 at a controlled predeterminedconstant rate of ilow through motor valve 52 in response to ow recordercontroller means 51. Quench oil from valve 52 is passed into a lowerportion of the oil body in separator 63, either through line 67 or 63,the latter being preferable. In this manner the unilashed oil inseparator 63 lis quenched to a temperature suchthat incipient crackingof this oil is prevented and thus does not take place while oil is onits way to the distillation chamber S via line 9. The rate of quench oilow is regulated to provide maximum temperatures of oil withdrawn fromseparator 63, without incipient oil cracking taking place. Generallyfrom 0.2 to 1.5 volumes of liquid quench is charged to separator 63 pervolume of unflashed oil Withdrawn therefrom. Quench oil added in thismanner to separator 63 also serves to act as 'a heat carrier during theinitial flashing step in section I of chamber 8, thus providing for anincrease in total heat available in the flash section and thereby for anincrease in depth of flashing ordinarily obtainable only at higher feedtemperatures. In conducting the quench, Ihave found it to beadvantageous to maintain the separator 63, or at least the portionthereof at its outlet, as an upright elongated vessel, and forintroducing the oil quench into a lower portion thereof to preventany,vapors whatsoever, formed by incipient cracking, to escape into line9 and ultimately reach vacuum jet 22, kthus preventing overloading ofthe jet and maintaining minimum operating pressures.

As a means for effecting further control of oil ternperature inseparator 63, if desired, a sidestream of oil from line 66 can berecycled through motor valve 71 in response to temperature recordercontroller means 79, line 69, cooler 72, and line 48 to separator 63, tothereby supplement control and maintenance of the predetermined,constant distillation feed temperature.

Vapors in section I containing entrained liquid droplets, are passeddownstream through bale T14 into shell section II, wherein somecondensation takes place by radiation, andpdue to residence time ofvapors therein at least a portion of entrainment therein settles asliquid product. Vapors freed from at least a portion of entrainment insection II are passed downstream through baffle 16 into section III incontact therein with a cooler oilspray from spray nozzle assembly 18,maintained at a temperature sufhciently lower than that of vaporscontacted therewith so as to eifect total condensation by heat exchange.Temperatures from to 300 F. are generally preferred.

Preferably, vapors are contacted against a ow of sprayed. oil invsectionIII, while maintaining the mo- 'mentum and directional ow conditions ofthe sprayed droplets as described above: When' not employing the coolerspray under the described flow `and momentum conditions, settling ofcondensate in section'III is somewhat more diicult, i. e., some liquidcondensate droplets may by their own momentum find their way into vacuumjet means 22 in which case efficiency of the vacuum producing means isgreatly impaired and concomitant high operating pressures areencountered with accompanying decrease in vacuum distillationefliciency.

Vacuum distillation zo'ne 8 is maintained under subatmospheric pressureby operation of vacuum jets 22, preferably steam jets, in directcommunication with shell section III at a point downstream from spraynozzle assembly 18,` via mist extractor21.

Liquid product of distillationis withdrawn from sections II and III,respectively, into surge vessels 24 and 26. Product from surge vessel24, comprises dirty gas oil and is advantageously recycled through motorvalve 32 in response to liquid level controller 28 via line 73 to heater59, i. e., together with fresh feed, and ultimately to vacuumdistillation chamber 8.

The portion of oil residuum product in surge vessel 23 not returned toseparator 63, is passed through motor valve 31 in response to liquidlevel controller 27 via l-ine 74 to a further utility not shown.

Condensed liquid distillation product in surge vessel 26 is particularlysuitable as feed to various hydrocarbon conversion processes, and iswithdrawn in a major proportion through line 76 and passed through line47 and through motor valve 4.3v in response to flow recorder controllermeans 49 at a carefully controlled rate of constant iiow to a catalyticcrackingV step as feed thereto. This control of gasoil flow through line47 to catalytic cracking is particularly of great importance when thesaid catalytic cracking is a TCC cracking system, the latter requiringan accurately controlled'feed inlet-flow rate; thus if the streamflowing in line 47 were regulated in response to a liquid level controlmeans, for `example liquid levelcontroller 29, the iiow to the catalyticcracker would vary slightly with change in composition of feed to thefurnace or with furnace temperature or other factors, which variancewould be undesirable.

A proportion of the liquid product in surge vessel 26 is recycled vialine 38 to lines 34,- 36 and 37 and cooler 40 as cooled feed to spraynozzles 18a, 18band 18C. Predetermined rates of flow of oil through eachof lines34, 36, and 37 are maintained through motor valves 43, 44, and46 respectively, in responseto flow recorder means 39, 41, and 42,respectively. Oil feed to spray assembly 18C is additionally cooled,upon bein'gp'a'ssed through cooler 45, to insure sufiicient finalcooling, when necessary, to effect total condensation. Remaining oilproduct in surgevessel 26 is passed through motor valve 33 at a ratecontrolled` in response to liquid level controller 29, via line 30 toheater 59 together with fresh feed, and ultimately to vacuumdistillation zone 8. This latter stream is generally a relatively smallproportion of product withdrawn from surge vessely 26. Y Y Y Whendesired, distillate recycled in line 30, or vgas oil recycled in line73, or-both, can be passed to heater 83 through lines 81 and 82respectively and heated therein and then admixed with heated feed inline 62. I

By the arrangement of baffles and condensing sprays in the distillationsystem as disclosedherein, a lower pressure drop across vthe chamber isachieved, than heretofore possible, for example a pressure drop acrossthe vessel 8 is generally in the order of about 0.3 to 4.0 mm. Hg.Accordingly, higher vacuum is obtained than heretofore possible, theover-all operating pressure being generally within the limits of 0.05vto l0 mm. Hg. Further, by the novel step of recycling residuum to thehot oil separator as a distillation feed quench and as a heat carrier,as described hereinabove, maximum possible ash feed ternperatures(without cracking) are achieved, and greater depth of flashing iseffected than obtainable at a given 6 Y temperature; offf'ee'din thevline to the flash zone without recycleiof residuum.

The method and apparatus of thisv invention are particularly suited forapplication in methods and apparatus as described and claimed in thecopending applications Serial No. 188,604 filed October 5, 1950 of V. C.Cavin et al., now abandoned andSerial No. 241,183 filed August l0, 1951of Paul M. Waddill, now abandoned.

In accordance with process and apparatus disclosed in application,Serial No. 188,604, a heavy oil is vacuum distilled byfirst, flashing itso as to effect partialvaporization; removing entrained liquid dropletsfrom vapors thus formed, by passing the said vapors against animpingingv oil spray maintained at a temperature and under momentumconditions so as to cause settling of the entrainment with substantiallyno condensation of the vapors; thereafter condensing resultingliquid-free vapor in contact with one or more cooler impinging oilsprays maintained under momentum conditions to cause settling ofcondensate formed, or by contacting such liquid-free vapors first with acooler condensing surface and then with an impinging oil spray to settlethe condensate formed. In another embodiment, residuum recovered fromthe flashing step isfurther reducedi'n a second stage, in a separatevessel employing entrainment removal and condensation steps similar tothose of the first'stage.

In accordance'with process and apparatus disclosed in application,Serial No. 241,183, a heavy oil is vacuum distilled by flashing, removalof entrainment, and subsequent condensation, in accordance with theprocess and apparatus of Serial No. 188,604 except that a second stagedistillation of first stage residuum product is effected in the samevessel in which the first stage reduction is effected, or in a separatevessel, in either case utilizing only one source of vacuum, this latterfeature being possibly by taking advantage of the inherent pressure dropacross the first stage distillation zone. Supplemental heating ofresiduum charged to the second stage distillation can be dispensed with.Distillation temperatures lower than employed heretofore are provided,while maintaining the pressure substantially unchanged, by dispersingthe oil feed in a highly finely divided state. y

Variation and modification are possible within the scope of theforegoing disclosure, drawing, andthe appended claims to theinvention','the essence of which is process and apparatus for effectingvacuum distillation of heavy oils; applicants process comprisingintroducing a heatedV heavy o il into a first kand upstream-most sectionof a substantially horizontal elongated distillation zone under flashingconditions causing partial feed vaporization, passing vapors containingventrained droplets of unvaporized feed downstream through a bafiie intoand through an Vadjacent and second section wherein condensation ofvapors can take place by radiation and some entrainment may settle fromthe vapors together with condensate, passing vapors from the said secondsection through a baffle downstream into an adjacent and third sectionin contact with a spray of cooler oil to effect substantially totalvapor condensation, quenching heated oil feed to n temperaturepermitting maximum non-cracking of the feed rby admiXing apredeterminedproportion of relatively cool Vrecycle residuum distillation 'producttherewith, the added residuum also serving asa heat carrier f during'theysubsequent flash distillation step to provide for an increased depth offlashing without necessitating-anv increase in feed temperature;applicants apparatus comprising a substantially horizontal elongatedshell, baffles in said shell dividing it into a plurality of sections,conduit means for introducing feed into an end section of the said shellin a direction toward the shell end thereof, preferably'against a wiremat therein, spray 'means in the opposite shell end section, vacuumproducing means in direct communication with the interior of the saidopposite shell end section and outlet conduit means in each of the saidshell end sections.

The temperature to which oil is quenched in the bottom of the hot oilseparator is generally in the range of 650 to 830 F., depending upon therefractoriness of the particular oil being processed.

As vapors pass through baffles 14 and 16 the tortuous path provided bythem serves to coalesce or remove a substantial portion or all of theentrained liquid droplets from the vapor stream. The removed liquidflows from the baffles to the bottom of the flash distillation vessel.

I claim:

1. ln the recovery of condensed product of vacuum distillation andfurther utilization of a portion of same as feed to a conversion steprequiring a constant feed inlet rate, the improvement comprisingcontinuously withdrawing and collecting such condensed product from thezone of said distillation, continuously passing a portion of thecollected condensate to said utilization at a predetermined constantrate controlled by the operation of an automatic flow control means, andcontinuously passing another portion of said collected condensate tosaid distillation zone in admixture with fresh feed thereto at a ratecontrolled in response to liquid level of the body of collected liquid.

2. 1n a process for the vacuum distillation of oils wherein oil to bedistilled is preheated to a temperature approximating that at whichincipient oil cracking occurs and is then charged to a vacuum ashingzone, the improvement comprising withdrawing a stream of unvaporized oilfrom the zone of said dashing and admixing same with oil heated as abovedescribed in proportions to quench said heated oil to a temperaturebelow that at which incipient cracking of same occurs and passing theresulting admixture to said vacuum flashing zone, whereby the presenceof light cracking product in the vacuum distillation feed is preventedand higher vacuum is obtained during said flashing, and oil adrnixedwith said feed acts as a heat carrier to provide for an increased depthof flashing without the need for an increase in feed temperature.

3. A vacuum distillation process comprising heating an oil to be vacuumdistilled, to an elevated temperature; passing oil thus heated into aseparation zone to separate any vapors therefrom; withdrawingunvaporized oil from said separation zone together with residualdistillation product admixed therewith as described hereinafter;introducing oil thus withdrawn into a vacuum distillation zone underflashing conditions so as to vaporize a portion of same, resultingresiduum oil settling in said distillation zone; condensing vaporsformed during said ashing and recovering resulting condensate; passing aportion of oil residuum from the zone of said ashing into admiXture withheated oil in said separation zone in an amount and at a controlled rateof flow so as to quench said heated oil therein to a temperature belowwhich incipient cracking of same takes place, and to act as a heatcarrier during said dashing; and recovering a remaining portion of saidresiduum.

4. The process of claim 3 wherein said residuum oil is introduced intoadmixture with said heated oil at a point in close proximity to thepoint of withdrawal of said heated oil from said separation zone. i

5. The process of claim 3 wherein a side stream of heated oil iswithdrawn from said separation zone, cooled, and then recycled into saidseparation zone so as to supplement said quenching.

6. The process of claim 3 wherein the said amount of oil residuumadmixed with heated oil is from 0.2 to 1.5 volumes per volume of saidunvaporized oil withdrawn from said separation zone.

7. A vacuum distillation chamber comprising a closed elongated shell; arst conduit extending into said shell and terminating in a rst endsection thereof; a rst baffle transversely closing said shell andterminating the said first end section; a second baille in said shellintermediate said rst bale and the shell end opposite said irst endsection, and terminating a second shell end section, and together withsaid first bafe defining a central shell section; spray means in saidsecond end section directed toward said second baffle; dam meansassociated with each of said baiiles to prevent ow of liquid within saidshell from any one of said shell sections into another shell section;vacuum producing means external to said shell, in direct communicationwith the interior of said second end section; a surge drum connectedwith an outlet conduit from said second end section; outlet conduitmeans in a side wall of said surge drum; a second conduit, connectedwith a surge drum outlet conduit; a third conduit, connected with asurge drum outlet conduit; means for controlling liquid llow from saidsurge drum through said second conduit in response to liquid level insaid surge drum; and means for controlling flow of liquid from saidsurge drum through said third conduit at a predetermined constant rate,said surge drum having a much smaller horizontal cross sectional areathan said second end section.

8. ApparatusV comprising a distillation chamber; a liquid outlet surgedrum connected with a liquid collecting section of said chamber; a firstconduit in communication with the interior of said drum at apredetermined point therein so as to convey liquid ow from said drum; asecond conduit in communication with the interior of said first conduit;means for controlling ilow of liquid through said second conduit at apredetermined constant rate; and means for controlling iow of liquidthrough said first conduit in response to a level of said liquid in saiddrum; said surge drum having a much smaller capacity and horizontalcross sectional area than said liquid collecting section.

References Cited in the file of this patent UNlTED STATES PATENTS2,018,778 Ebner Oct. 29, 1935 2,125,325 Youker Aug. 2, 1938 2,151,310Aldridge et al Mar. 21, 1939 2,185,222 Nofsinger et al. J'an. 2, 19402,357,113 Houghland et al. Aug. 29, 1944 2,443,970 Waddill lune 22, 19482,459,404 Anderson Ian. 18, 1949 2,575,051 Egger et al Nov. 13, 1951

3.A VACUUM DISTILLATION PROCESS COMPRISING HEATING AN OIL TO BE VACUUMDISTILLED, TO AN ELEVATED TEMPERATURE; PASSING OIL THUS HEATED INTO ASEPARATION ZONE TO SEPARATE ANY VAPORS THEREFROM; WITHDRAWINGUNVAPORIZED OIL FROM SAID SEPARATION ZONE TOGETHER WITH RESIDUALDISTILLATION PRODUCT ADMIXED THEREWITH AS DESCRIBED HEREINAFTER;INTRODUCING OIL THUS WITHDRAWN INTO A VACUUM DISTILLATION ZONE UNDERFLASHING CONDITIONS SO AS TO VAPORIZE A PORTION OF SAME, RESULTINGRESIDUUM OIL SETTLING IN SAID DISTILLATION ZONE; CONDENSING VAPORSFORMED DURING SAID FLASHING AND RECOVERING RESULTING CONDENSATE; PASSINGA PORTION OF OIL RESIDUUM FROM THE ZONE OF SAID FLASHING INTO ADMIXTUREWITH HEATED OIL IN SAID SEPARATION ZONE IN AN AMOUNT AND AT A CONTROLLEDRATE OF FLOW SO AS TO QUENCH SAID HEATED OIL THEREIN TO A TEMPERATUREBELOW WHICH INCIPIENT CRACKING OF SAME TAKES PLACE, AND TO ACT AS A HEATCARRIER DURING SAID FLASHING; AND RECOVERING A REMAINING PORTION OF SAIDRESIDUUM.